James, I'm not totally sure what you're asking but basically either way this isn't the place to ask.
If you're speaking literally and you're asking if you can
make a game in Blender, then the answer is no, of course not! Blender is not made as a game creation tool, so the answer is naturally no. If this was your question, it is totally irrelevant and shouldn't have been asked here.
If you're asking if you can use models made in Blender, sort of. Exporting directly to .x will not work because it encodes the file differently to FPSC, so if you wanted a Blender model in FPSC I'm fairly sure you would have to export it as .3ds and then convert it.
Evil has a new name. Demo out now!